This application is based on Patent Application No. HEI 10243850 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an image reading apparatus and specifically relates to art for detecting the shape of a document in an image reading apparatus of a type in which document are placed face upward.
2. Description of the Related Art
In conventional image reading apparatus of a type in which document are placed face upward, the shape of a document surface is detected using a sensor. The detection result is used to accomplish focus adjustment when reading the document, as well as curvature correction and condensation correction of the read document. The sensor for detecting the shape of the document in the height direction is a contact-type sensor, such that the sensor for document detection is provided on the document platen so as to detect the shape of a document in the height direction based on the coordinate position of a pin in contact with the document. Non-contact type sensors use a laser beam to detect the shape of a document in the height direction via a Doppler effect, or use a light source to illuminate the top edge of a document so as to detect the shape of the top edge of the document by reading the image of the top edge of the document reflected on a reflection member.
The image reading apparatuses of the aforesaid type which detect the shape of a document in the height direction by having a document detection pin come into contact with the document placed on the document platen are disadvantageous inasmuch as the document may be damaged by the document detection pin. Furthermore, in image reading apparatuses which detect the shape of a document in the document height direction using a laser beam, and image reading apparatuses which read the image of the top edge of a document illuminated by a document-illuminating light source via a reflection panel, there may be a detection error in detecting the shape of the document in the height direction depending on the color of the document because the shape of the document in the height direction is detected using light. Furthermore, the light may disadvantageously cause deterioration of them document.
Consideration has been given to not detecting the shape of a document in the height direction until the reading start instruction has been issued to prevent light-induced deterioration of the document, but in this case an operator cannot be alerted to the document placement direction on the document platen until a reading start instruction is issued.
An object of the present invention is to provide an improved image reading apparatus which eliminates the aforesaid disadvantages.
Another object of the present invention is to provide an image reading apparatus capable of accurately detecting the shape of a document in the document height direction regardless of the color of the document.
Another object of the present invention is to provide an image reading apparatus capable of detecting the shape of a document in the document height direction without causing deterioration or damage to the document.
Yet another object of the present invention is to provide an image reading apparatus having improved operating characteristics by alerting an operator to an abnormal document placement condition before the reading start instructions are issued.
These objects are attained by providing an image reading apparatus for optically reading a document from above, said image reading apparatus comprising: a document platen for placing a document, an image sensing device for reading an image of a document placed on the document platen, and at least one ultrasonic sensor for emitting ultrasonic waves to a document placed on the document platen and detecting the shape of the document in the document height direction based on the reflected wave from the document.
In this construction, and ultrasonic wave is emitted from the ultrasonic sensor toward a document placed on the document platen, and the distance data from the ultrasonic sensor to the document are detected based on the time differential of the reflected wave from the document. Furthermore, the position of the document can be detected based on the strength or weakness of the reflected wave from the document. In this way the shape of the document in the document height direction can be detected without using light. Moreover, the shape of the document in the document height direction can be accurately detected regardless of the document color.
The shape of a document in the document height direction can be detected without causing deterioration or damage to the document by detecting the shape of a document in the document height direction using an ultrasonic sensor. In this way an operator can be alerted to an abnormal document placement conditions by detecting the shape of a document in the document height direction before the reading start instruction is issued.
The ultrasonic sensor may be rotated or moved to detect the shape of the document in the height direction. In this way the shape of a document in the document height direction can be accurately detected.
Furthermore, a plurality of stationary ultrasonic sensors may be provided so as to detect the shape of a document in the document height direction by switching the ultrasonic sensor used for detection. In this way the shape of a document in the document height direction can be accurately detected with the same effectiveness as rotating or moving the ultrasonic sensor.